I really liked the 2 sirens storyline that they showed in ep 4. At first Sybil felt like a very average.. mehh.. kinda villain but this Seline is pretty crazy. I don't know how strong Cade, the Devil, will be but he doesn't look very intimidating as of now.
Also I feel (wish/hope) Katherine will be back. The way Georgie was dragged into hell was quite similar to the way Katherine was dragged into God-knows-where in season 5.